This application claims the priority of German patent document 198 01 393.0, filed Jan. 1, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a steering system of a motor vehicle whose steered vehicle wheels are coupled during normal operation, with a steering handle (for example a steering wheel) by an electronic regulating system that constantly checks for correct function, and regulates a steering actuator which is connected with and adjusts the steered vehicle wheels. For this purpose a steering angle setpoint generator is actuated by the steering handle, and a steering angle setpoint sensor is actuated by the steered vehicle wheels. The regulating system also regulates a manual force setting device connected with the steering handle to simulate a steering resistance. For this purposes, a manual force set value sensor detects the forces transmitted between the steering actuator and the steered vehicle wheels, as well as a manual force actual value sensor that detects forces transmitted between the manual force adjusting device and the steering handle.
During abnormal or emergency operation, the steered vehicle wheels are forcibly coupled, especially mechanically or hydraulically for adjusting the steering by the steering handle.
Steering systems have been developed for future motor vehicles that operate by the "steer by wire" concept, at least during normal operation. Such systems, which are described for example in German patents documents DE 42 32 256 A1, DE 195 40 956 C1, and DE 195 46 942 C1, offer the basic advantage that they are suitable without design modifications, for a wide variety of vehicles, at least in terms of the regulating system and associated sensing system. By appropriate programming, practically any translation ratio can be produced between the adjusting stroke of the steering handle and the change in the steering angle of the steered vehicle wheels. In addition, it is possible to connect the regulating system with additional sensors in order to automatically take into account or adjust for parameters to be set, for example side wind influences.
In order to ensure a satisfactory degree of safety in the event of system errors, provision can be made to automatically switch to an operating mode for abnormal operation or emergency operation if an error occurs in the regulating system or if the signals evaluated by the regulating system are absent. In this operating mode, forced coupling between the steering handle and the steered vehicle wheels can be provided so that this steering system theoretically operates like a conventional steering system, but the usual mechanical steering column found in conventional steering systems can be replaced by other mechanical systems or even by hydraulic, especially hydrostatic systems.
According to German patent document DE 195 40 956 C1 referred to above, a mechanical connection between the steering handle and the steered vehicle wheels is provided for emergency operation. For this purpose a clutch, which normally keeps this mechanical connection separated, is closed in an emergency to produce the mechanical forced coupling between the steering handle and the steered vehicle wheels. A servo valve that is inactive during normal operation is located in the mechanical connection between the steering wheel and the steered vehicle wheels, by which valve the hydraulic steering actuator provided for normal operation can be actuated as a conventional servo valve.
In German patent document DE 195 46 942 C1, a hydraulic rod between the steering handle and the steered vehicle wheels becomes effective in an emergency, so that a double-acting compressing element actuated by the steering handle is forcibly connected hydraulically with another compressing element coupled with the steered vehicle wheels.
In a conventional power steering disclosed in German DE 44 22 383 C1, the steering wheel is continuously forcibly connected mechanically with the steered vehicle wheels to adjust their steering. A servo valve system, which is actuated as a function of steering forces transmitted between the steering wheel and the steered vehicle wheels, controls a hydraulic servo motor so that the manual forces to be applied to the steering wheel for an individual steering maneuver are reduced to a greater or lesser degree. In addition, an electric motor that is free of self-locking, and can act on the steering wheel, is controlled as a function of the signals from a manual force sensor associated with the steering wheel and/or as a function of the steering forces acting on the steered vehicle wheels. In this manner, it is assured that the feedback forces which are perceptible in the steering wheel are comparable to the steering forces acting on the steered vehicle wheels. In addition, if the hydraulic servo system should fail, the electric motor can operate as an emergency servo motor.
The goal of the present invention is ensure greater safety for a steering system of the type recited at the outset.
These and other objects and advantages are achieved by the vehicle steering system according to the invention, in which upon forced coupling of the steering handle and the steered vehicle wheels, a manual force actual value sensor detects the steering forces transmitted between the steering handle and the steered vehicle wheels and controls the regulating system, with sufficient functional ability. A manual force adjusting device, and/or the steering actuator functions in the manner of a servo motor, to reduce the manual forces required for steering maneuvers.
For abnormal operation or emergency operation, a hydraulic forced coupling is provided between the steering handle and the steered vehicle wheels, and pressure sensors are mounted on a hydraulic system that produces the hydraulic force coupling, for detecting leaks. In this manner, during hydraulic forced coupling of the steering handle and the steered vehicle wheels signals can be derived from the signals of these sensors, which are correlated with forces transmitted between the steering handle and the steered vehicle wheels.
The present invention is based on the general idea of using a sensor associated with a steering handle, whose signals are correlated with the manual forces exerted on the steering handle, to determine the forces transmitted between the manual force adjusting device and the steering handle during normal operation and to determine the forces transmitted between the steering handle and the steered vehicle wheels during abnormal operation. In the former case the manual forces can be regulated by analogy with a steering resistance to be simulated, and in the latter case the manual forces required for steering actuation of the steered vehicle wheels can be reduced as in the case of a conventional power steering system. According to the invention, an especially high degree of safety is ensured because sensors that monitor the tightness of the hydraulic emergency system during normal operation, and thus are themselves constantly monitored for functional ability, are available for further tasks in emergency operation, namely detecting the steering forces acting on the steered vehicle wheels.
Thus, it is assured with a maximum degree of reliability that the emergency system can operate as a power steering system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.